1. Field of the Invention
This invention relates to an automatic exposure control system for a camera provided with a day-light exposure range and with a flash exposure range, and more particularly, to a flash exposure time range bracketing device incorporated in the automatic exposure control system in order to insure that the formation of a correct flash exposure aperture is effected with a shutter time which is involved in a possible flash exposure time range and which is either dependent on, or independent, of the setting of shutter dial when the shutter dial is in a position providing a shutter time within or outside the above-identified range respectively.
2. Description of the Prior Art
It has been the practice of the prior art in making flash exposures between day-light exposure to manually readjust the shutter dial of a camera to a particular shutter time, for example, 1/60 second or 1/125 second at which it is assured that the shutter slit has an effective area large enough to unblock the entire area of one film frame. The constantly necessary readjustment of the shutter dial constitutes, for the photographer, a troublesome manipulation which when overlooked will cause an introduction of an incorrect shutter time value to the exposure control system of the camera. In addition to this, there is some possibility of occurrence of an accidentally incorrect setting of the shutter dial after the necessary manipulation has been made for flash photography.
For a solution of these problems, the prior art has proposed the provision of an additional timing circuit arranged in an automatic exposure control circuit to operate independently of the intrinsic timing circuit cooperative with the shutter dial and constructed to form only one exposure interval of, for example, 1/60 second adapted for use in flash photography. Although the selection of either the additional or the intrinsic timing circuit for cooperation with an electronic switch controlling the period of actuation of the shutter of a camera can be manually or automatically made by means of a circuit-transfer switch, the exposure control circuit of such construction does not permit for the photographer to modify the particular flash exposure time by taking into account the lighting condition of the environment surrounding an object of principal flash photographic interest, or to make flash exposure under ambient or day-light illumination, namely, what is called "day-light-synchro" flash exposures. In order to make "day-light-synchro" flash exposures, therefore, the additional timing circuit must be cut off from the exposure control circuit, and then the day-light exposure range is rendered operative while the shutter dial is being readjusted to select an exposure time from a series of bracketed exposure times ranging, for example, from 1/4 second to 1/60 second based on his personal experience. When this manipulation of the shutter dial is overlooked in switching the camera from the day-light exposure range to the flash exposure range, in the case where the preceeding day-light exposure was made with an exposure time outside a possible flash exposure time range, no correct flash exposures can be made, as the additional timing circuit for flash photography works to no purpose.